Cache JSON view in nodejs/express app

json_cache_view.js

/**
 * viewFunc(req, res, caching) in which caching is a function to return a value
 * to be cached.
 *
 * @param key
 * @param req
 * @param res
 * @param time
 *    if `time` < 0 then no caching
 *    if `time` = 0 then caching permanently
 *    if `time` > 0 then caching within `time` seconds
 * @param viewFunc
 */
var cacheView = function(key, req, res, time, viewFunc) {
  if (time < 0) {
    return viewFunc(req, res, function(){});
  }

  cache.get(key, function(err, value) {
    if (!err && value) {
        return res.send(JSON.parse(value));
    } else {
      viewFunc(req, res, function(newValue) {
        if (newValue instanceof Object) newValue = JSON.stringify(newValue);

        cache.set(key, newValue);
        if (time > 0) cache.expire(key, time);
      });
    }
  });
};

// Example usage
exports.get_all_sources = function(req, res) {
  cacheView('sources', req, res, 0, function(req, res, caching) {
    var fields = 'name homePage description status lastUpdated';

    Source.find({status: 'enabled'}).select(fields).exec(function(err, sources) {
      if (err) return res.send(500, {error: err});

      var data = {sources: sources};

      caching(data);
      return res.send(data);
    });
  });
};